C ++检查类对象是否包含某个元素

Question

Lets say i Have a class like this

class Person 
{
private:
  int id;
  string name ,lastname;
  vector<Person> likedperson;
public:
//getter setters
}

how to check likedperson has a certain id like

Person user;
if(user.likedperson.contains(34))
    //do stuff
else 
    //do stuff 

Answer 1

You want to use std::find_if that uses a UnaryPredicate, something like:

if (std::find_if(std::begin(likedperson), std::end(likedperson), 
    [](const Person& p) -> bool { return p.id == 34; }) != std::end(likedperson)) {

Answer 2

Unlike some languages, C++ mostly separates the algorithms that operate on containers (things that store data) from the containers themselves.

There's a standard algorithm to find an element, if it exists, in any container: std::find . (See http://en.cppreference.com/w/cpp/algorithm/find for more details.)

You want something like

if (std::find(likedperson.begin(), likedperson.end(), 34) != likedperson.end())